I waver between the cheaper coastal sub and the standard. Early on I figured that even though the coastal sub would sink with one hit, it was cost effective if it could stay at sea for even a couple or three turns. But now I've gone more to the standard sub, which can take a hit without sinking, figuring that the likelihood of two hits in one turn is low, so I should be able to keep that type of sub afloat for many turns (with repairs).

On the other hand, for the cost of repairs, I could just build another coastal sub.

Perhaps there should be a substantive advantage of one type of sub over another.

Didn't want to state an opinion since I am kind of biased because of our ongoing game. But when looking at build time and cost then it appears that regular subs are about 2.5 times more expensive and about the same factor longer to build than coastal subs. In exchange they have 2.0 times the hit points. Given the hassle and cost of repair I would argue in favor of coastal submarines since most of the convoy routes pass through coastal seas anyways at the beginning of the campaign (in the Med and around UK / France / Portugal).

But maybe I am missing some other stats differences that are not obvious such as how successful the different subs types are at detection of enemy vessels, interception of convoys etc. Couldn't find this in the manual either. Would be nice to get some complete unit statistics.